drm/i915: Add WARN_ON in intel_get_crtc_for_pipe()

Add a WARN_ON for a disabled pipe in pipe_mask at
intel_get_crtc_for_pipe() function.

v2:
- Use drm_WARN_ON instead of WARN_ON.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200224124004.26712-7-anshuman.gupta@intel.com

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1415,6 +1415,9 @@ intel_get_first_crtc(struct drm_i915_private *dev_priv)
 static inline struct intel_crtc *
 intel_get_crtc_for_pipe(struct drm_i915_private *dev_priv, enum pipe pipe)
 {
+	/* pipe_to_crtc_mapping may have hole on any of 3 display pipe system */
+	drm_WARN_ON(&dev_priv->drm,
+		    !(INTEL_INFO(dev_priv)->pipe_mask & BIT(pipe)));
 	return dev_priv->pipe_to_crtc_mapping[pipe];
 }